This invention relates to hand tools, and more particularly to torque wrenches.
A torque wrench is a hand tool which allows the user to tighten a threaded fastener to a predetermined torque. Using a torque wrench helps prevent over-tightening which can lead to stripping of threads, break-off of fasteners or other difficulties. It also helps prevent under-tightening which can result in the fastener failing to perform, such as by working itself loose over time.
Generally an inexpensive variety of torque wrench in prevalent use is the "beam" type shown in FIG. 1 and designated 10. At one end, a male socket head 12 is provided for use with interchangeable sockets (not shown). A handle 14 is located at the other end, with a straight beam 16 interposed between the socket head 12 and the handle 14. The beam 16 is a metal rod, for example, having a cylindrical geometry with a length of approximately 15 to 24 inches (38 to 61 cm). A dial 18 is affixed to the beam 16 at a point adjacent to the handle 14. A needle, or pointer 20 is secured at or near the socket head 12, extending towards the handle 14, parallel to the beam 16, and culminating at its free end with a marker or point 22 situated within a slot or elongate window 24 in the dial 18. The slot 24 extends generally in a direction perpendicular to the beam 16.
In use, the beam-type torque wrench 10 is secured to a threaded fastener (not shown), such as a hexagonal headed bolt or screw or a nut by means of interchangeable sockets attached to the socket head 12. An operator turns the wrench 10 via handle 14 in either of the directions indicated by the arrows "a" or "b", and thereby tightens or loosens the fastener. During tightening, the torque wrench 10 fulfills its primary purpose by providing a read-out or display of the torque applied to the fastener. Initially during tightening of the fastener, substantially all manually applied torque results in a turning of the socket head 12. At some point, however, the turning of the wrench 10 by handle 14 results in not only the turning of the socket head 12, but also a bending or bowing of the beam 16. For example, this can occur when the fastener starts to seat. During this condition, the end of the beam 16 adjacent the handle is displaced in the direction of arrow "a" relative to the remainder of the beam 16. Since needle 20 floats at its distal end, being not attached at that end to the beam 16, the needle's marker 22 moves relative to the dial's scale. When the user sees that the needle has swung to a pre-selected torque read-out, the fastener has been tightened to the proper amount.
Other types of torque wrenches are also known. For example, dial-type and adjustable torque wrenches are intended for more professional mechanics. These torque wrenches are generally more expensive than beam-type wrenches, although the former are typically more accurate and sensitive, and sometimes more delicate than beam-type wrenches.
An object of the invention is to provide a relatively inexpensive torque wrench; one which can be used and discarded by purchasers of products requiring assembly using a torque wrench.
A further object of the invention is to provide a torque wrench of simple yet rugged design which can be readily manufactured and then packaged without the need for specialized packing materials to protect the torque wrench during transit.